Electronic elevator speed control

ABSTRACT

An improved electronic elevator speed control of the type which controls the deceleration of the car as a function of time from a fixed point short of each landing, accommodates for short runs under high-speed operation where full speed is not obtained before deceleration must be initiated. If a timer, which begins timing a fixed interval when the car is started, does not time out before a stop signal is generated, the speed of the car is limited and the RC time constant of the circuit which controls the deceleration of the car from the fixed point short of the landing is adjusted to provide a slower rate of deceleration. A substantially constant rate of acceleration is achieved regardless of the speed to which the car is being accelerated by charging a pattern-generating capacitor toward a voltage in excess of the maximum speed desired and then limiting the charge on the capacitor by connecting clamping diodes between the capacitor and taps on a voltage divider having a potential proportional to the desired speed. A resistor in series with a Zener diode shunting the pattern generator power supply accommodates for changes in the motor field current caused by fluctuations in line voltage.

tlnited States Patent [72] Inventors Alvin O. Lund Little Falls; Milton Fink, Rochelle Park, N.J.; Stephen J. Greenfield, Rochester, NY. [21] Appl. No. 879,727

{22] Filed Nov. 25, 1969 [45] Patented Aug. 17, 1971 73] Assignee Westinghouse Electric Corporation Pittsburgh, Pa.

[54} ELECTRONIC ELEVATOR SPEED CONTROL 6 Claims, 2 Drawing Figs.

[52] US. Cl. 187/29 R [5 1] Int. Cl B66b 1/28 [50] Field of Search 187/29 {56] References Cited UNITED STATES PATENTS 3,523,232 8/1970 Hall et at. 187/29X AC SOURCE at Primary Examiner-Gris L. Rader Assistant Examiner-W. E. Duncanson, Jr. Att0rneysA. T. Stratton, C. L. Freedman and R. V.

Westerhoff I ABSTRACT: An improved electronic elevator speed control of the type which controls the deceleration of the car as a function of time from a fixed point short of each landing, accommodates for short runs under high-speed operation where full speed is not obtained before deceleration must be initiated. If a timer, which begins timing a fixed interval when the ear is started, does not time out before a stop signal is generated, the speed ullhe car is limited and the R( time eon stunt of the circuit which controls the deceleration of the car from the fixed point short of the landing is adjusted to provide a slower rate of deceleration. A substantially constant rate of acceleration is achieved regardless of the speed to which the car is being accelerated by charging a pattern-generating capacitor toward a voltage in excess of the maximum speed desired and then limiting the charge on the capacitor by connecting clamping diodes between the capacitor and taps on a voltage divider having a potential proportional to the desired speed. A resistor in series with a Zener diode shunting the pattern generator power supply accommodates for changes in the motor field current caused by fluctuations in line voltage.

FULL WAVE RECTIFIER PATTERN GENERATOR ELECTRONIC ELEVATOR SPEED CONTROL BACKGROUND OF THE INVENTION 1. Field ofthe Invention This invention relates to a motor control system and has particular relation to elevator speed control systems wherein both acceleration and deceleration are controlled as a function of time.

2. Description of the Prior Art Providing for smooth accurate landings is one of the most perplexing tasks in the field of elevator design. A great many elevator speed control systems provide for the control of deceleration of the car as either a stepwise or continuous function of the distance remaining to the point at which the car is to be stopped. A simpler and widely used system in elevators in the 200 ft./min. or lower class controls deceleration as a function of time to slow the car smoothly from full speed at a fixed point short of the landing to a safe landing speed. An example of such a system is disclosed in U.S. Pat. No. 2,508,179 wherein a speed reference signal is generated as a function of time in the form ofa voltage across a capacitor. For deceleration the capacitor is permitted to discharge through a resistor selected to give the desired rate of deceleration. An improved version of this system which provides for adjustment in the rate of acceleration as the car approaches full speed, and in the rate of deceleration as the car approaches landing speed, is disclosed in U.S. Pat. No. 2,620,898.

In the systems disclosed in the abovementioned patents, the car always has sufficient time to reach its rated speed before deceleration must be initiated. When these systems are adapted to higher speed operation wherein the car does not reach full speed before it reaches the fixed deceleration point short of the next landing, the landing characteristics for short runs becomes undesirable. Since deceleration is initiated at the same fixed distance from the landing but the speed from which the car must be decelerated is less, utilization of an electronic circuit with the same RC time constant as for the higher speed run, causes the car to very quickly slow down to landing speed and then creep into the landing. This greatly increases the time for the car to land thereby tying up the car unnecessarily and delaying service. The systems which control deceleration as a function of the distance remaining adjust the point at which deceleration is initiated depending upon the speed of the car. This necessarily adds to the complexity and therefore the cost of such systems.

SUMMARY OF THE INVENTION According to this invention the rate of deceleration of the car is adjusted if the car has not reached full rated speed prior to reaching the fixed point short of a landing at which the car is to stop. Preferably the speed control has a first and a second mode of operation. Under the first mode of operation, the maximum speed obtainable is limited to a first maximum and the rate of the deceleration is adjusted to provide for a smooth prompt slow down from this first predetermined maximum speed at the fixed point to a safe landing speed. Under the second mode of operation, the speed of the car is limited to a second predetermined maximum which is the full rated speed of the system and the rate of deceleration is adjusted to pro vide for an acceptable rate of deceleration from said second maximum speed at the fixed point. Deceleration is initiated under both modes of operation in response to the generation of a slow down signal as the car passes the fixed point short of the landing at which the car is to make a stop. The slowdown signal can only be generated in response to an enabling signal which is generated by the supervisory system before the car reaches the appropriate fixed point.

Preferably the speed control system is biased to the first mode of operation. Transfer means are provided for transfer ring the speed control to the second mode of operation when it is apparent that the car will be able to reach full speed before deceleration for a stop will have to be initiated. In the embodiment of the invention disclosed, a timing interval is initiated when the car is started. If an enabling signal is not generated before the timer times out, the speed control will be shifted to the second, or high-speed mode of operation.

In the preferred embodiment of the invention, the speed control signal is represented by the voltage across a capacitor. A constant rate of acceleration, regardless of the maximum speed desired, is obtained by charging the capacitor toward a voltage in excess of the voltage representative of the full rated speed. Clamping diodes connected to taps on a voltage divider limit the voltage on the capacitor to values corresponding to the desired maximum speeds. The different rates of deceleration are obtained by discharging the capacitor through resistive circuits having the desired time constant.

In addition, means are provided to stabilize the speed of the motor despite fluctuations in line voltage. In the preferred embodiment of the invention, a resistor in series with a Zener diode shunting the voltage inputs to the pattern generator, varies the pattern voltage in inverse proportion to the change in motor speed accompanying variations in the line voltage.

It is therefore a first object of the invention to provide an improved elevator speed control of the type which initiates deceleration a fixed distance from a landing, which accommodates for short runs wherein deceleration must be initiated before acceleration has been completed.

It is another object of the invention to provide an improved speed control as described in the first object which accommodates for a short run by varying the time rate of deceleration.

It is a further object of the invention to provide an improved elevator speed control which provides a constant rate of acceleration regardless of the maximum speed to which the elevator is to be accelerated.

It is a still further object of the invention to provide an improved motor speed control of the type wherein the motor field and the speed pattern generator are supplied by a common voltage source, which stabilizes the speed of the motor against variations in the voltage source.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic diagram of an elevator system em bodying the invention with portions shown in block diagram form.

FIG. 2 is a circuit diagram in straight line form ofa portion of the elevator system illustrated in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT In order to simplify the presentation, the invention will be described as applied to the elevator system disclosed in the Lund U.S. Pat. No. 2,620,898. Only a discussion of those portions of the system necessary for an understanding of the present invention will be described herein in detail. Although the system under discussion is attendant operated, it will be appreciated by one skilled in the art that the invention is equally applicable to fully automatic elevator systems.

Referring to the drawings, FIG. 1 shows an elevator car C which is connected to a counterweight CW through a suitable flexible rope or cable 11 which passes around the sheave 13. The car C is suspended for movement in a vertical direction to serve a plurality of floors four of which are shown. In order to facilitate the accurate landing of the elevator car at a desired floor, various expedients known to the prior art may be employed. For the purpose of discussion, it will be assumed that the car C carries two inductor relays ll. and 2L. The operation of these inductor relays is well known in the elevator art. In brief, although the coil of the inductor relay is energized, the individual contacts will not be operated until the relay passes in close proximity to an inductor plate which completes the magnetic circuit for those contacts.

The inductor relay IL is a leveling relay which cooperates with pairs of inductor plates P1 and P2 at each floor to level the car. The inductor relay 2L is intended to initiate decelera- P4 which are mounted in the elevator hatch for each floor of the associated building. As shown in FIG. 1 the inductor plates P3 cooperate with the slowdown inductor relay 2L to initiate slowdown of the elevator car as the car approaches a floor traveling in the up direction. Similarly the inductor plates P4 cooperate with the inductor slowdown relay 2L to initiate slowdown of the elevator car as it approaches a landing from above. Since the invention relates to high speed systems, it will be noticed that the inductor plate P3 between the second and third landing, which cooperates with the slowdown inductor relay 2L to bring the car to a stop at the third floor while traveling in the up direction, is closer to the second floor than to the third floor. This is required because in the higher speed systems it takes a substantial distance to bring the car smoothly to a stop without discomfort to the passengers. It can be seen therefore that if a car departed from the second floor for the third floor, it would travel a very short distance before deceleration for the landing at the third floor would be initiated. It is the primary object of this invention to accommodate the operation of the system to compensate for this condition.

Referring to the description of the system, the sheave 13 is mounted on a shaft 15 which is driven by a direct current motor MO. The armature of the motor MO is connected in a loop circuit with the armature of a direct current generator G in the familiar Ward-Leonard configuration. The armature of the generator G is rotated by a suitable electric motor (not shown) at a constant speed. The voltage output of the generator, which determines the speed of rotation of the motor MO, is governed by control of the field winding of the generator G. One such winding GF2 is shown in FIG. 1. Current for the generator winding GF2 is derived from an alternating current source through a power modulator and appropriate direction circuits. The Lund Pat. describes in detail a power modulator employing grid-controlled rectifier tubes of the gaseousdischarge type known as thyratrons. Other types of power modulators such as the solid state unit disclosed in US. Pat. No. 3,470,434, issued to William R. Caputo on Sept. 30, l969 and assigned to the same assignee as this application can also be readily adapted for use in this system.

The power modulator is controlled in a familiarmanner by an error signal which is derived from a pattern signal representative of the desired speed of the motor and feedback signal which is representative of the actual speed of the motor. The pattern signal from the pattern generator shown in the righthand side of FIG. 1, is applied across the buses 61 and 63 as in the Lund patent. The feedback signal representative of the actual speed of the motor is derived from the back electromotive force (EMF) circuit illustrated in the Lund patent. The pattern signal and the feedback signal are summed in opposition to each other through appropriate contacts of the direction relays and the resultant error signal is applied to the power modulator through the conductor 57. A direct current bias for the thyratrons is applied through the resistor 102 as in the Lund patent. This bias signal would not be required with the solid-state power modulator ofCaputo.

The pattern signal is generated in the form ofa voltage appearing across an energy storage device such as the capacitor 67. Acceleration is controlled by controlling the rate at which the capacitor 67 is charged. Deceleration is controlled through a controlled discharge of the capacitor 67. The heart of the pattern generator is a voltage divider composed ofthe serially connected resistors R3, R4, R5, R8, R9 and R10. The voltage divider is powered by a full-wave rectifier which is shunted by a filtering capacitor C1.

The capacitor 67 is charged as the car is started through the resistor R1, variable resistor R2, contacts 55-1 of the overspeed relay, contacts 0R9 of the speed control relay and the resistor R10. As will be seen from reference to the Lund patent, the speed control relay GR is energized when the car is started on an interfloor run and remains energized until deceleration is initiated. The time rate of buildup of the charge on the capacitor 67, and therefore the rate of acceleration, can be adjusted by manipulation of the tap on the variable resistor R2. The capacitor 67 will therefore charge toward the voltage which appears between the junctions A and B on the voltage divider. This voltage is selected to be substantially higher than the actual maximum pattern voltage desired so that the system will operate in the substantially linear portion of the familiar exponential RC charging curve for the capacitor 67.

The actual maximum voltage to which the capacitor 67 will be charged is determined by the taps C and D on variable resistors R5 and R6 and the contacts OF2 of the one-floor relay, The variable resistor R5, which is in series with the resistor R4, is shunted by the series combination of variable resistor R6 and resistor R7. With the contacts OF2 open it can be seen that the voltage across the capacitor 67 will be limited to the voltage between the variable tap D on variable resistor R6 and the junction B. The diode D1 permits the rate at which the voltage accumulates on the capacitor 67 to be controlled by the resistors R1 and R2 since no current can flow from the variable tap D to the capacitor 67. The voltage on capacitor 67 will therefore charge at a rate determined by the resistors R1 and R2 toward the voltage AB but will be clamped at the voltage db. With the contacts OF2 closed, the voltage on capacitor 67 will be clamped at the voltage CB determined by the positioning of the variable tap C on the variable resistor R5. The values of the resistors R4, R5, R6 and R7 are selected so that the potential of the tap C will always be below that of the tap D. Again the diode D2 assures that the capacitor 67 will be charged at a rate determined by the resistors R1 and R2.

During deceleration when the contacts GR9 are open and the contacts GR10 are closed, the rate of deceleration is controlled by the discharge of the capacitor 67 through the resistor R10, variable resistor R12 and, when the contacts OF3 are open, the resistor R11. With the contacts OF3 closed, the capacitor 67 will discharge at a more rapid rate through the resistors R10 and R12. The variable resistor R12 may be adjusted to provide the desired maximum deceleration.

Two values of minimum speed are provided during the deceleration phase. As long as the make contacts 22-1 of the door preopening relay are closed, the voltage on the capacitor 67 will not be permitted to drop below the potential between junction B and a tap E on the variable resistor R8. Despite this clamping of the minimum speed during door preopening, the rate of deceleration to this speed is determined by the resistors R10, R12 and in some cases R11, by the diode D3 which prevents discharge of the capacitor through the variable resistors R8 and R9. This variable tap assures that the car will retain a certain intermediate speed after the slowdown point so that a prompt landing will be achieved.

It is common practice in the elevator field to initiate door opening as the car approaches a landing in order to minimize the time that the car remains at a floor. For passenger safety however it is necessary to assure that the car does not exceed predetermined speeds as the car levels with the door open. Therefore as the car approaches the floor and the doors begin to open, the contacts 22-1 will open so that the minimum speed will be determined by the voltage between the junction B and the tap F on the variable resistor R9. Again the diode D4 assures that the rate at which the car decelerates to the minimum speed is determined by the resistors R10, R12 and in some cases R11 rather than by the resistor R9.

When a common direct current supply is utilized to supply the energization for the pattern generator and the motor field circuit, it is desirable to provide for adjustments in the pattern voltage to compensate for the effect variations in supply voltage will have on the operation of the motor. For instance, should the supply voltage increase, the pattern voltage will increase thereby calling for the motor to turn at a higher speed. The increase in supply voltage will at the same time increase the motor field current. The increase in magnetic flux in the motor caused by this increase in field current will tend to slow the motor down. Unfortunately, however, this slowdown in the speed due to the increase in the motor field current does not offset the increase in speed caused by the increase in pattern voltage. Therefore, it is desirable to attenuate the effect on the pattern voltage caused by variations of the supply voltage.

It is common practice today to stabilize a voltage source with a Zener diode. As is well known, the Zener diode will block the flow of current in a given direction until the voltage across the device reaches the Zener breakdown voltage at which time a further attempt to raise the voltage across the device will result only in increased current flow. By itself the Zener diode Zll would cooperate with the resistor R3 to maintain a constant voltage between the junctions G and H on the voltage divider. When the supply voltage increased, the Zener Z1 would maintain a constant voltage between the junction G and H by shunting current between these junctions so that the increase in voltage from the source would be reflected in the voltage drop across the resistor R3. By adjusting the normal voltage of the voltage source to be substantially above the Zener voltage, constant voltage could be maintained across the voltage divider. By placing the resistor R13 in series with the Zener Z1, fluctuations in the supply voltage above the Zener voltage are reflected in the form of the voltage drop across the resistor R13 caused by the current passed by the Zener diode Z1. The value of the resistor R13 is selected so that the increase in the pattern voltage associated with the increase in the supply voltage is sufficient to offset the tendency for the motor to slowdown caused by the associated increase in motor field current.

It was assumed for the purposes of simplifying this description that the circuits of the system disclosed in U.S. Pat. No. 2,620,898 were utilized to illustrate the operation of the present invention in a working elevator system. Referring to FIG. 2, it will be seen that certain additional relays are neces sary for the operation of the present invention. They may be powered by the same buses, Bl and B2, that energize the circuits of the patent. The voltage across these buses is a direct current voltage rectified from a three-phase source. The field coil MF of the motor MO is connected directly across the busses B1 and B2.

The one floor relay OF is energized either through the make contacts URS of the up direction relay or the make contacts DRS of the down direction relay and the make contacts N6 of the running relay. The circuits for these relays may be found in the patent. It is sufficient to say that the auxiliary running relay N is energized whenever the motor MO is running. Since the system described in the patent is an attendant-operated system, the up direction relay UR or the down direction relay DR is energized as long as the attendant holds the car switch in the up or down direction position. The attendant holds the switch in the desired position as long as the car is to continue in the given direction. When the attendant desires that the car be stopped he center the car switch thereby deenergizing the appropriate direction relay as he approaches the selected landing. The car will continue to run however, but the centering of the car switch serves as an enabling signal for the automatic landing system which will bring the car to a stop at the landing.

The relay OF is not energized immediately upon the closure of the contacts URS or DRS and the contacts N6. The circuit must be completed through these contacts for a given interval before the timer will be operated to complete the circuit between the buses B1 and B2 to energize the relay OF. Such timers are well known. Any type oftimer providing the desired timing accuracy may be employed. The timer interval is selected so that it times out just before the car reaches the fixed point at which deceleration would have to be initiated if the car was going to stop at the next floor. Preferably it should time out while the cat is still accelerating at a constant rate toward the one-floor run speed to avoid jerk when the system switches to the high-speed mode. Once the relay OF is energized it is held in through its holding contacts CPI and the contacts N6 of the auxiliary car running relay. It is clear then that the relay OF will be energized a predetermined time after the attendant moves the car switch to the up or down position in order to initiate movement of the car. However, it is also clear that if the attendant moves the car switch to the neutral position before the predetermined interval has expired that the relay OF will remain deenergized.

The relay 22 is the door preopen relay commonly utilized in present day elevator systems. For purposes of this disclosure the relay 22 is energized through the make contacts L2 of the leveling relay. Reference to the patent will show that these contacts are closed while the car is running but that they will open when the car approaches within approximately 7 inches ofthe landing at which the car is to stop. Deenergization of the relay 22 causes the car doors to begin opening so that by the time the car reaches the landing the doors are substantially open. This expedites the transfer of passengers through the doorway.

The overspeed relay S5 is energized through the normally closed switch OS on the speed governor. Such switches are well known in the elevator art and are commonly set to open when the speed of the car exceeds the normal rated speed by 10 percent. Therefore, it will be seen that the overspeed relay 55 is normally energized but will be deenergized when the car overspeeds.

OPERATIONS It would be useful at this point to describe a few typical operations of the system. Assume initially that with the car at the first floor, the attendant desires to travel to the fourth floor. With the car at rest at the first floor, the contacts URS and DRS of the up and down direction relays and the contacts N6 of the auxiliary car running relay are open so that the onefloor relay OF will be deenergized. Under these conditions. the overspeed relay 55 will be energized while the door preopen relay 22 will be deenergized. Furthermore, with the car at rest the speed control relay GR will be deenergized so that the contacts GR9 are open and contacts GRlO are closed.

When the attendant moves the car switch to the up position, the up direction relay UR will be energized to close the contacts URS. As will be seen for the Lund patent this will result in energization of the auxiliary car running relay N so that the contacts N6 will be closed. This ill initiate the OF timer. As will also be seen from the Lund patent, the speed control relay GR will be energized at this time to close the contacts GR9 and open the contacts GRlf). This will cause the capacitor 67 to begin to charge through the resistor R1, variable resistor R2, contacts 55-l and GR9 and resistor R10. As the capacitor begins to charge the voltage thereon will be impressed on the power modulator through the leads 61 and 63. This impressed voltage will cause the power modulator to energize the generator field GFZ in such a manner as to cause the generator to apply a voltage to the motor MO in the proper sense to cause the car to begin to accelerate in the up direction. As the car accelerates, the back EMF circuit will generate a signal proportional to the actual speed of the motor. This signal will be summed with the pattern signal and the resultant signal will control the power modulator. Since the pattern signal will exceed the feedback signal at this point, the car will continue to accelerate. The capacitor m will continue to charge at a rate determined by the resistors R1, R2 and R10 toward the voltage determined by the tap C on the variable resistor R5 since the contacts OF2 ofthe one-floor relay are closed at this time. However, since the attendant maintains the car switch in the up position so that the contacts URS remain closed, at the end of the predetermined interval. the OF timer will time out thereby energizing the relay OF. Energization of this relay results in the closing of the holding contacts OH to bypass the contacts URS. This will result in opening of the OFZ contacts which will permit the capacitor 67 to continue charging at the rate determined by the resistors R1, R2 and R toward the voltage determined by the tap D on the variable resistor R6. Energization of the relay OF will also result in closing of the contact OF3 which has no effect on the system at this point. The voltage on the capacitor will build up to the voltage determined by the tap D, and when the car has reached maximum speed the signal generated by the EMF circuit will balance the voltage on the capacitor 67 so that the power modulator will supply only sufficient energization to the field OF2 to maintain the car at constant speed.

As the car proceeds up in the hatchway and passes the inductor plates P3 and P4 between the first and second floor, and between the second and third floor there will be no effect on the system as long as the attendant maintains the car switch in the up position. As the car passes the third floor the atten dant will center the car switch. Since the relay OF remains energized through the holding contacts OFl, the centering of the car switch which deenergizes the up direction relay has no immediate effect on the speed of the car. The centering of the switch does, however, energize the slowdown inductor relay 2L. Therefore, as the relay 2L passes in close proximity to the inductor plate P3 between the third and the fourth floor the speed control relay GR is deenergized. This results in the opening of the contacts GR9 and closing of the contacts GRlO. This will cause the capacitor 67 to begin to discharge through the contacts GRlO, resistor R10, variable resistor R12 and the contacts OF3. The variable resistor R12 is adjusted so that with deceleration initiated from the fixed point determined by the inductor plate P3 the speed of the car will he smoothly and promptly reduced from full speed. With the door preopening relay 22 energized at this point, the tap E on variable resistor R8 will assure that the voltage on capacitor 67 is not dropped below a predetermined minimum which will bring the car to the floor promptly. The deenergization ofthe speed control relay GR as the car passes the fixed point determined by the inductor plate P3, will result in energization of the leveling inductor relay 1L. As will be seen from the Lund patent, when the car approaches within approximately 7 inches of the fourth floor, the magnetic circuit for the contacts on the leveling inductor relay 1L will be completed by the plate P2 which will in turn result in deenergization of the leveling relay L. When the contacts L2 close, the door preopening relay 22 will be deenergized to initiate door opening. In addition, the contacts 22-1 will open thereby causing the capacitor 67 to further discharge to the voltage corresponding to the landing speed determined by the tap F on the variable resistor R9. When the car arrives at a point level with the landing the direction circuits will disconnect the pattern generator from the power modulator. The stopping of the car will result in the deenergization of the auxiliary car running relay N to open the contacts N6 thereby deenergizing the relay OF and resetting the OF timer.

It can be seen from the circuits of FIG. 1 that should the car overspecd causing the ()5 switch to open thereby deenergiling the overspeed relay 55, thc contacts 55-! would open and the contacts 55-2 would close causing the capacitor 67 to discharge through the resistors R8 and R9 thereby lowering the pattern potential to the point determined by the potential at the junction J on the voltage divider. This will permit the car to continue the trip but at a greatly reduced speed.

Assume now that with the car at the first floor the attendant desiring to move the car to the second floor, places the car switch to the up position thereby energizing the up direction relay UR. As will be evident from the above discussion, this will result in energization of the auxiliary car running relay N so that with the contacts URS and N6 closed the timer begins timing its predetermined interval. in the same manner as previously described the capacitor 67 will begin charging from the power supply through the resistor R1, variable resistor R2, contacts 55-1 and GR9, and resistor R10. This charging voltage will appear on the leads 61 and 63 and through the direction circuit will apply a signal to the power modulator through the lead 57 which will energize the generator field GF2 with the proper polarity to cause the generator to apply a voltage to the motor armature causing the car to begin to travel in an up direction. As the car begins to move, the back EMF generated by the motor will be summed with the pattern signal, however, since the pattern signal will lead the feedback signal the car will continue to accelerate. The rate of charging capacitor 67 is selected in a manner to cause the capacitor to charge toward the voltage AB at a rate which will cause the car to accelerate quickly and smoothly.

Since it was assumed that the car is to stop at the second floor, the attendant will center the car switch after the car has begun to move. This will have no immediate effect on the speed of the car, however, it will cause the contacts URS of the up direction relay to open. Since the timing interval has not expired at this point the relay OF will remain deenergized. With OF deenergized the contacts OF2 will remain closed and the contacts OF3 will remain open. At this point the contacts GR9 remain closed and the capacitor 67 continues to charge at a rate determined by the resistors R1, R2 and R10. With the contacts Of2 closed however, the maximum voltage on the capacitor 67 will be clamped to the voltage determined by the tap C on the variable resistor R5. As the car continues to accelerate, the feedback signal generated by the EMF circuit will increase until it balances the voltage on the capacitor 67 at which point the car will maintain constant speed.

As the car continues upward in the hatchway, the inductor relay 2L mounted on the car and which was energized when the car switch was placed in the neutral position by the attendam, will pass in close proximity to the plate P3 between the first and second floor. As mentioned above, this will result in deenergization ofthe speed control relay GR thereby opening the contacts CR9 and closing the break contacts GR10. Since the potential at the junction K at this point is equal to potential of the tap C on the variable resistor R5, the capacitor will begin to discharge through contacts GRIO, resistor R10, variable resistor R12 and the resistor R11. With the resistor R11 in the circuit the capacitor will discharge at a slower rate than it would if the contacts OF3 were closed. As the voltage on the capacitor decreases thereby causing a decrease in the potential across the buses 61 and 63, the feedback signal will exceed the pattern signal and the power modulator will be energized in a manner which will cause a reduction in the generator field OF2 thereby causing the motor to slow down in compliance with the reduced pattern voltage. As the pattern voltage decreases, the tap E on the variable resistor R8 will assure that the pattern voltage does not drop below a predetermined speed to assure that the car arrives promptly at the landing.

When the car reaches a point approximately 7 inches from the landing, the contact L2 on the leveling relay will open to deenergize the door preopening relay 22. Opening of the break contacts 22-1 permits the voltage on the capacitor 67, and therefore the command speed, to drop to a point determined by the tap F on the variable resistor R9. This is the same landing speed at which the car approached the fourth floor in the above high-speed example, however, on the short run the car approaches this speed at a slower rate although deceleration is initiated the same distance from the landing.

Although the invention was described as being adapted for use with the attendant operated system disclosed in the Lund patent, the invention is equally applicable to fully automatic systems. In such systems the stopping signal performing the function of the attendant in centering the car switch is automatically generated by the supervisory system as the car approaches a landing. One skilled in the art with the benefit of this disclosure could readily adapt the invention for use with such fully automatic systems.

We claim as our invention:

1. An elevator system comprising a structure having a plurality of landings, an elevator car, motive means for moving the elevator car relative to the structure to serve the landings, said motive means including speed control means having a first mode of operation which includes control of the deceleration of the elevator car as a first function oftime in response to a slowdown signal and a second mode of operation which includes control of the deceleration of the elevator car as a second function of time in response to a slowdown signal, stopping means for stopping the elevator car at selected landings including slowdown means for generating a slowdown signal a fixed distance from a selected landing, and transfer means responsive to the number of landings to be traversed between stops for transferring the speed control means between said first and second modes of operation.

2. The combination of claim 1 wherein the stopping means includes means for generating an enabling signal for rendering the slowdown means effective only as the elevator car approaches a selected landing, and wherein the transfer means includes means responsive to the generation of an enabling signal while the elevator car is still accelerating for rendering the transfer means ineffective for transferring the speed control means from the first to the second mode of operation.

3. The combination of claim 1 wherein the stopping means includes means for generating an enabling signal for rendering the slowdown means effective as the elevator car approaches a selected landing and wherein the transfer means includes a timer which begins timing a predetermined interval when the elevator car is started and means responsive to the timing out of said timer before the stopping means generates an enabling signal for transferring said speed control means from the first mode of operation to the second mode of operation.

4. The combination of claim 3 wherein said predetermined interval is less than the interval required for said motive means to accelerate the car to full speed.

5. The combination of claim 4 including means biasing the transfer means to the first mode of operation and wherein said speed control means includes means controlling the acceleration of said elevator car at a predetermined rate with respect to time, means limiting the maximum speed obtainable under said first mode of operation to a first predetermined speed,

and means limiting the maximum speed obtainable under the second mode of operation to a second predetermined speed which exceeds said first predetermined speed and said combination wherein the speed control means also includes means with a first time constant and responsive to a slowdown signal to control the rate of deceleration of the elevator car under said first mode of operation from said first predetermined speed at said fixed point to a landing speed adjacent to the selected landing and means with a second time constant which exceeds said first time constant to control the rate ofdeceleration of the car under said second mode of operation from said second predetermined speed at said fixed point to said landing speed adjacent the selected landing whereby the elevator car is accelerated to the respective predetermined maximum speeds at substantially the same rate under either mode of operation while deceleration, which is initiated at the same fixed distance from the selected landing under either mode of operation, is adjusted to bring the elevator car promptly and smoothly to the landing despite the variation in the speed of the elevator car when deceleration is begun under the respective modes of operation.

6. The combination of claim 5 wherein the acceleration pattern is generated as a function of the voltage across an energy storage device said combination including the energy storage device, a power supply, a charging circuit for charging said energy storage device from said power supply toward a voltage in excess of a voltage proportional to the maximum speed desired, a voltage divider connected across said power supply and having taps producing voltages proportional to the maximum speeds desired under said first and second modes of operation of the speed control, and voltage clamping means connected to the energy storage device and said taps for clamping the voltage across said energy storage device to voltages corresponding to the maximum speed desired under the selected modes of operation, 

1. An elEvator system comprising a structure having a plurality of landings, an elevator car, motive means for moving the elevator car relative to the structure to serve the landings, said motive means including speed control means having a first mode of operation which includes control of the deceleration of the elevator car as a first function of time in response to a slowdown signal and a second mode of operation which includes control of the deceleration of the elevator car as a second function of time in response to a slowdown signal, stopping means for stopping the elevator car at selected landings including slowdown means for generating a slowdown signal a fixed distance from a selected landing, and transfer means responsive to the number of landings to be traversed between stops for transferring the speed control means between said first and second modes of operation.
 2. The combination of claim 1 wherein the stopping means includes means for generating an enabling signal for rendering the slowdown means effective only as the elevator car approaches a selected landing, and wherein the transfer means includes means responsive to the generation of an enabling signal while the elevator car is still accelerating for rendering the transfer means ineffective for transferring the speed control means from the first to the second mode of operation.
 3. The combination of claim 1 wherein the stopping means includes means for generating an enabling signal for rendering the slowdown means effective as the elevator car approaches a selected landing and wherein the transfer means includes a timer which begins timing a predetermined interval when the elevator car is started and means responsive to the timing out of said timer before the stopping means generates an enabling signal for transferring said speed control means from the first mode of operation to the second mode of operation.
 4. The combination of claim 3 wherein said predetermined interval is less than the interval required for said motive means to accelerate the car to full speed.
 5. The combination of claim 4 including means biasing the transfer means to the first mode of operation and wherein said speed control means includes means controlling the acceleration of said elevator car at a predetermined rate with respect to time, means limiting the maximum speed obtainable under said first mode of operation to a first predetermined speed, and means limiting the maximum speed obtainable under the second mode of operation to a second predetermined speed which exceeds said first predetermined speed and said combination wherein the speed control means also includes means with a first time constant and responsive to a slowdown signal to control the rate of deceleration of the elevator car under said first mode of operation from said first predetermined speed at said fixed point to a landing speed adjacent to the selected landing and means with a second time constant which exceeds said first time constant to control the rate of deceleration of the car under said second mode of operation from said second predetermined speed at said fixed point to said landing speed adjacent the selected landing whereby the elevator car is accelerated to the respective predetermined maximum speeds at substantially the same rate under either mode of operation while deceleration, which is initiated at the same fixed distance from the selected landing under either mode of operation, is adjusted to bring the elevator car promptly and smoothly to the landing despite the variation in the speed of the elevator car when deceleration is begun under the respective modes of operation.
 6. The combination of claim 5 wherein the acceleration pattern is generated as a function of the voltage across an energy storage device said combination including the energy storage device, a power supply, a charging circuit for charging said energy storage device from said power supply toward a voltage in excess of a voltage proportional to the maximum speed desired, a voltagE divider connected across said power supply and having taps producing voltages proportional to the maximum speeds desired under said first and second modes of operation of the speed control, and voltage clamping means connected to the energy storage device and said taps for clamping the voltage across said energy storage device to voltages corresponding to the maximum speed desired under the selected modes of operation. 